Referring to FIGS. 1, 2 and 3, there are shown exemplary block diagrams of radio access networks for three different wireless technologies. FIG. 1 shows a UMTS (universal mobile telephone system) network 10 where user equipment 12, depending on location, wirelessly communicates with one of two base transmitting stations 14. The base stations, in turn, communicate with a radio network controller/base station controller (RNC/BSC) 16. The RNC/BSC communicates with a serving GPRS support node (SGSN) 18 which communicates to a gateway GPRS support node (GGSN) 19. FIG. 2 shows a CDMA 2000 (also referred to as 3G1X) network 20 where user equipment 22 communicates with either a first or second base station 24. The base stations communicate with a base station controller/packet control function (PCF) device 26 which in turn communicates with a packet data serving node (PDSN) 28. FIG. 3, in a similar fashion to FIG. 2 shows an HDR (high data rate) network 30 in which user equipment UE1 32 may communicate with one of several base stations 34. The base stations 34 communicate to a BSC/PCF 36 which in turn communicates to a PDSN 38.
In current releases, the 3G1X backhaul (between BTS and RNC/BSC) network is based either on Frame Relay or ATM technology. An HDR backhaul network is based on IP technology over HDLC over narrowband links like T1/E1. For R99, UMTS a backhaul network is based on ATM technology.
Since the airlink capacity is improving in future releases e.g. for UMTS R99, the airlink capacity is approximately 1 Mbps per sector, but with HSDPA, capacity can reach up to 10 Mbps and there is a push to integrate 3G networks with WLAN networks. That is, there is interest in seeing an IP-based Radio Access Network and exploring the possibility of carrying backhaul traffic over metro-Ethernets. There are, however, additional requirements to reduce the packet loss during handoff or cell switching by deploying some multicast mechanisms.
As would be understood by a person skilled in the art, in HDR, there is no concept of a downlink soft-handoff as in 3G1X and UMTS. However, in HDR, the UE is allowed to switch from one BTS to another depending on the airlink quality. UE1 32, as shown in FIG. 3, will send signals to BTSs 34 within a given proximity to inform them which specific BTS it wants to communicate with at any particular time. This is referred to as HDR cell switching. The target BTS then informs the RNC when UE1 has chosen to communicate with it. Since there is typically a communications delay between BTS and BSC (about 20–40 ms round trip), this means UE1 can only switch from one BTS1 to BTS2, after approximately 50–100 ms round trip delay.
If a BSC can multicast UE bound traffic to two or more base stations in the neighborhood of UE1, and UE1 can inform the target BTS of the next radio link frame number it expects, then it is possible to have a faster response time for HDR cell switching. Without a native layer2 multicast service, however, one has to resort to higher layers, such as Layer 3 IPMulticast, to provide such a multicast feature, which is not as efficient. Accordingly, there is a need to provide a more efficient methodology for multicasting to desired sets of BTSs.